Integrated<i>K</i>-band spectra of old and intermediate-age globular clusters in the Large Magellanic Cloud

Lyubenova, M.; Küntschner, H.; Rejkuba, M.; Silva, David R.; Kissler-Patig, M.; Tacconi-Garman, L. E.; Larsen, Soeren S.

doi:10.1051/0004-6361/200913041

Cited by 21 publications

(27 citation statements)

References 69 publications

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“…In the case of CO 2.29 μm W λ , similar results were obtained by Lyubenova et al (2010, see their fig. 9) for old and metal‐poor Large Magellanic Cloud globular clusters.…”

Section: Resultssupporting

confidence: 86%

“…However, one advantage of the EPS models is their large range in ages and metallicities, while observed spectral libraries are restricted to the optical (e.g. Bica & Alloin 1986) or cover only small fractions of the NIR spectral region, like the region around the 1.6‐ and 2.29‐μm CO bands (Origlia, Moorwood & Oliva 1994; Origlia et al 1997) or only the K ‐band spectra (Lyubenova et al 2010).…”

Section: Introductionmentioning

confidence: 99%

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Near-infrared integrated spectra of Galactic globular clusters: testing simple stellar population models

Riffel

Ruschel-Dutra

Pastoriza

et al. 2010

Monthly Notices of the Royal Astronomical Society

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We present SOAR/OSIRIS cross‐dispersed near‐infrared (NIR) integrated spectra of 12 Galactic globular clusters that are employed to test Maraston NIR evolutionary population synthesis models, and to provide spectral observational constraints to calibrate future models. We measured equivalent widths (Wλ) of the most prominent NIR absorption features: λ 1.49 μm, Mg iλ 1.58 μm, Fe i/Mg i, λ 1.59 μm, Si i, λ 1.71 μm, Mg i, λ 2.21 μm, Na i and λ 2.26 μm, Ca i as well as the λ 1.62 μm, λ 2.29 μm, CO and λ 2.05 μm, CN molecular bands. Optical Wλ of G band (4300 Å), Hβ, Mg2, Fe i (4531, 527 and 5335 Å) and Na i (5897 Å) were also measured. The globular clusters Wλ were compared with model predictions with ages within 4–15 Gyr, and metallicities between 0.005 and 2 Z⊙. Observed integrated colours (B−V, V−I and V−Ks) were also compared with models. The NIR integrated spectra among our sample appear qualitatively similar in most of the absorption features. The Maraston models can properly predict the optical Wλ observed in globular clusters. Regarding the NIR, they do underestimate the strength of Mg i 1.49 μm, but they can reproduce the observed Wλ of Fe i 1.58 μm, Si i 1.59 μm and CO 2.29 μm, in about half of our sample. The remaining objects require the inclusion of intermediate‐age populations. Thus, we suggest that the presence of C‐ and O‐rich stars in models is important to reproduce the observed strengths of metallic lines. Another possibility is the lack of α‐enhancement in the models. In the case of the optical and NIR Fe i lines, standard models and those that include blue horizontal branch stars produce similar results. A similar trend is observed for Na i 5895 Å, while in the case of the G band, the models with blue horizontal branch do describe better the observations. For most of the sample, the optical to NIR colours are well described by the Maraston models. In general, Maraston models can provide reliable information on the NIR stellar population of galaxies, but only when Wλ and colours are taken together; in other words, Wλ and continuum fluxes should be simultaneously fitted. However, the results should be taken with caution, since the models tend to predict results biased towards young ages.

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“…In the case of CO 2.29 μm W λ , similar results were obtained by Lyubenova et al (2010, see their fig. 9) for old and metal‐poor Large Magellanic Cloud globular clusters.…”

Section: Resultssupporting

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Near-infrared integrated spectra of Galactic globular clusters: testing simple stellar population models

Riffel

Ruschel-Dutra

Pastoriza

et al. 2010

Monthly Notices of the Royal Astronomical Society

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“…Indeed, we chose a median stack instead of a sigma-clipped mean precisely because of its better performance in removing these artefacts from the stacked spectra, which is particularly important toward the red limit of the spectral range (near the FeH band). The error in the median is 1.25σ/N 1/2 (i.e., 25% larger than the error on the mean), where σ is the standard deviation in the stack of N spectra (Lupton 1993). The spectral resolution of each stacked spectrum is the quadratic mean of σ inst (λ), the dispersion of the line-spread function as a function of wavelength.…”

Section: Binning Proceduresmentioning

confidence: 99%

SDSS-IV MaNGA: the spatially resolved stellar initial mass function in ∼400 early-type galaxies

Parikh

Thomas

Maraston

et al. 2018

Monthly Notices of the Royal Astronomical Society

133

144

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MaNGA provides the opportunity to make precise spatially resolved measurements of the IMF slope in galaxies owing to its unique combination of spatial resolution, wavelength coverage and sample size. We derive radial gradients in age, element abundances and IMF slope analysing optical and near-infrared absorption features from stacked spectra out to the half-light radius of 366 early-type galaxies with masses 9.9 − 10.8 log M/M . We find flat gradients in age and [α/Fe] ratio, as well as negative gradients in metallicity, consistent with the literature. We further derive significant negative gradients in the [Na/Fe] ratio with galaxy centres being well enhanced in Na abundance by up to 0.5 dex. Finally, we find a gradient in IMF slope with a bottomheavy IMF in the centre (typical mass excess factor of 1.5) and a Milky Way-type IMF at the half-light radius. This pattern is mass-dependent with the lowest mass galaxies in our sample featuring only a shallow gradient around a Milky Way IMF. Our results imply the local IMF-σ relation within galaxies to be even steeper than the global relation and hint towards the local metallicity being the dominating factor behind the IMF variations. We also employ different stellar population models in our analysis and show that a radial IMF gradient is found independently of the stellar population model used. A similar analysis of the Wing-Ford band provides inconsistent results and further evidence of the difficulty in measuring and modelling this particular feature.

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“…Davidge (1990) obtained H-and K-band near-infrared spectra of four GCs in M31 and found that they exhibited strong CN absorption bands, as also seen in optical spectra (Burstein et al 1984;Schiavon et al 2013). Lyubenova et al (2010Lyubenova et al ( , 2012 obtained JHK integrated-light spectra of clusters in the Large Magellanic Cloud and found that a variety of features were well reproduced by simple stellar population models (Maraston 2005) for the old GCs in their sample. The spectra of intermediate-age clusters (1-2 Gyr) were less well reproduced, possibly because of difficulties with the modelling of carbon-rich stars.…”

Section: Introductionmentioning

confidence: 94%

Modelling of integrated-light spectra from the optical to the near-infrared: the globular cluster G280 in M31

Larsen

Pugliese

Brodie

2018

A&A

Self Cite

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Context. In previous papers, we introduced our method for measuring chemical abundances from integrated-light spectra of globular clusters and applied it to a variety of extragalactic star clusters. Our work so far, however, has concentrated primarily on the optical range 4200 Å-6200 Å. Aims. Here we extend our analysis technique to the infrared and test it on an H-band spectrum of the massive globular cluster G280 in M31. Methods. We simultaneously analyse an optical spectrum of G280, obtained with the HIRES spectrograph on the Keck I telescope, and an H-band spectrum obtained with NIRSPEC on Keck II. We discuss the sensitivity of our results to various modifications of the input assumptions, such as different line lists and isochrones and the possible presence of a metallicity spread in G280. Results. When using the most recent version of the Kurucz line list, we measure iron abundances of [Fe/H] = −0.68 ± 0.02 from the optical spectrum and [Fe/H] = −0.60 ± 0.07 from the infrared spectrum. These values agree well with previous spectroscopic determinations of the metallicity of G280. While the small difference between the optical and infrared measurements is insignificant given the uncertainties, it is also consistent with a metallicity spread similar to that observed in massive GCs such as ω Cen and G1, and also hinted at by the colour-magnitude diagram of G280. The optical and infrared spectra both indicate an α-enhancement of about 0.3-0.4 dex relative to solar-scaled abundances, as typically also observed in Milky Way GCs. Conclusions. From this analysis, it appears that our integrated-light analysis technique also performs well in the H-band. However, complications due to the presence of molecular bands and telluric contamination are more severe in the infrared, and accurate modelling of the coolest giants is more critical.

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IntegratedK-band spectra of old and intermediate-age globular clusters in the Large Magellanic Cloud

Cited by 21 publications

References 69 publications

Near-infrared integrated spectra of Galactic globular clusters: testing simple stellar population models

Near-infrared integrated spectra of Galactic globular clusters: testing simple stellar population models

SDSS-IV MaNGA: the spatially resolved stellar initial mass function in ∼400 early-type galaxies

Modelling of integrated-light spectra from the optical to the near-infrared: the globular cluster G280 in M31

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